This invention is directed to a method and apparatus for processing intelligent network calls within a telephone switching system in an exchange, and in particular, to a method and apparatus for operating an access subsystem and interconnection subsystem within the switching system to more efficiently filter calls and control traffic load.
An intelligent network based switching system architecture offers greater flexibility to the telephone service providers to design, implement and market new services in a relatively short time.
In addition, certain types of telephone customers, such as, companies running telephone call-in contests, certain 1-800 numbers or even certain central office codes within densely populated areas receive more telephone calls (load) than others, or more than is desirable for the efficient operation of the overall telephone switching system responsible for directing calls to these particular numbers. To protect the telephone network from congestion due to overload or failure conditions, it is known in the art to utilize call filtering techniques. Filtering may be applied on a system wide basis, or telephone companies may also offer services that allow particular subscribers to have filtering applied to their incoming calls.
Conventional telephone switching systems achieve high performance and economic design by using a system architecture as shown in FIG. 1, that includes modular access subsystems that contain switching elements, network interface elements, and other hardware and software for routing incoming calls to desired subscribers. A switching system 10 may include a plurality of access subsystems 12 (1-N) to support all the lines and trunks served by the telephone exchange. The access subsystems also include software controlled processors 13 that provide call processing and management functions for the subsystem. The telephone switch system 10 within the exchange may also include an interconnection subsystem 14 operatively coupled to the N access subsystems 12 to provide connectivity between the individual access subsystems and to provide certain overall management functions, such as fault management. Interconnection subsystem 14 also includes a processor 15 for processing of calls and performing management functions.
The switching system described above utilizes filtering functions which are best suited for us in an intelligent network as shown in FIG. 5. An intelligent network allows a switch to directly operate on a call. Different tasks associated with an incoming call may be done by different parts of the intelligent network. Intelligent networks calls require processing and are designed to be processed at least minimally by the switching system 10. Non-intelligent network calls may be handled entirely at the local exchange. In the intelligent network, a plurality of switching systems 10 will be associated with a service control point (SCP) 22. Conventionally, the service control point communicates with the access subsystems 12 of base switching system 10 to provide service control functions to the switching system 10. This allows switching system 10 to focus on service switching rather than the service control process. In the prior art, when a call arrives switching system 10 first analyzes the digit to determine whether this call is an intelligent networking type of call. Digits such as 1-800, 1-900 or 0 usually signal an intelligent network call. For example, dialing 0 may result in an automated response from an operator determining whether incoming call is to be a calling card call, a collect call, a person to person call or the like. If the switching system 10 determines that the incoming call is an intelligent network call it forwards the call to SCP 22 to determine what specific actions it should take. SCP 22 instructs the switch and/or other intelligent network elements known as intelligent peripherals regarding the necessary actions to be taken. Intelligent peripherals may include the voice activated responses for an automated operator to prompt the caller to take the necessary action at their end; such as dialing the calling card number and PIN number.
In an intelligent network it becomes critical that the switching system spend as little time as possible in a given call and immediately interact with the SCP to handle the call. One method known in the art for implementing the intelligent network functions in a switching system constructed as in switching system 10 is to centralize the intelligent networking functions in interconnection subsystem 14. As the intelligent networking inquiries are similar in operation to the filtering activities as discussed above and in fact, the filtering process discussed above may in fact be considered a subset of the intelligent network functions operation on intelligent network calls may be handled in a generally similar way. Accordingly, upon receipt of an incoming call, the access subsystem 12 would send a query to the interconnection subsystem 14 for each incoming call to determine whether the call should be treated as an intelligent networking call. The information subsystem would analyze the call by comparing the digits in the call to a list of intelligent network matching criteria to determine whether the incoming call is an intelligent network call. If it is determined that a match has occurred and an intelligent network call is present, the interconnection subsystem 14 determines the type of intelligent network call and sends this information to SCP 22. SCP 22 will then return information regarding processing of this call. As with filtering, although this process centralizes the function of processing intelligent network calls, it overloads one portion of switching system 10 causing a bottle neck at interconnection subsystem 14.
Call filtering is a selective acceptance of calls that meet specific filtering criteria. Filtering criteria typically include a number of digits that are compared to the called number. Selective acceptance of calls that meet the filtering criteria may be done by a number of methods, the most common of which are interval-based filtering or ratio based filtering. By way of example, for interval based calling for controlling the load to a highly called exchange, the switching system should accept only a specified number of the calls that meet the filtering criteria, i.e., match the filtered number, during each interval of a specified duration; such as one call per second. For ratio based call filtering or absolute number call filtering, the switching system within the exchange accepts only a specified ratio of the calls that meet the filtering criteria such as one call out of every four or only the first ten callers. Such a filtering criteria is particularly useful in a situation in which a particular subscriber may be running a telephone contest such as the first ten callers to a radio station. If a call is not passed by the exchange, it is blocked and the caller typically hears a tone indicating busy or an announcement.
To implement filtering, it is known in the art to centralize the filtering function in interconnection subsystem 14. A library of filtering criteria is stored in interconnection subsystem 14. An incoming call is received by the access subsystem 12. The access subsystem 12 sends a query to interconnection subsystem 14 for each incoming call attempt Interconnection subsystem 14 would then compare the incoming call to a list of numbers to be filtered (filtering criteria) such as a specific number for a mass call-in or specific types of 1-800 numbers or area codes. If it was determined that the number was the type subject to filtering, interconnection subsystem 14 would then determine whether or not this was the Nth call for that particular number and then make a determination whether or not this particular incoming call should be blocked either by the interval based call filtering or the ratio based call filtering method. Interconnection subsystem 14 also makes a count of the incoming calls matching a particular criteria so that it may determine whether or not the next call should be blocked according to the associated filtering methods.
The determination of interconnection subsystem 14 regarding whether the call is to be passed or blocked is then transmitted to access subsystem 12 and access subsystem 12 either blocks or passes the call in response to the instructions from interconnection subsystem 14.
This method has been satisfactory. However, putting the entire filtering function in interconnection subsystem 14, slows down the overall operation of the system because of the necessity to query interconnection subsystem 14 for each and every call whether filtering applies or not. This turns interconnection subsystem 14 into a bottle neck for the overall exchange. The effect is to slow down the exchange to such an extent that the system may crash. Accordingly, it is desired to provide a method for filtering calls in a telephone exchange which overcomes the shortcomings of the prior art.
Accordingly, it is also desired to provide a structure and method for operating an intelligent network which overcomes the shortcomings of the prior art.